timber nor steel industry which could compete in size with surrounding countries, nor a need to import large quantities of costly raw materials or sophisticated chemicals.
Further, ferrocement construction could serve not only the building industry but at the same time could also be easily linked with shipbuilding and tank or bulk storage container production.
In such cases a production yard could, in times of slackening of de- mand for one item be easily adopted to produce another, since it deals with basically simple and chemically un- sophisticated processes, where opera- tives require only medium grade skills. The land application could also in- clude: prefabricated light-weight floor- ing units particularly attractive when used in ever higher office blocks; roofing both in-situ and pre-fabricated utilising both shell principles and hanging construction; facing panels used both as reinforcement and per- manent shuttering; and one to three- storey prefab housing, especially suit- ed for outlaying districts.
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Regarding roofing alone it is worth- while to mention that in comparison with the lightest reinforced and pre- stressed concrete construction in U.S.S.R. the use of ferrocement in industrial roofs resulted in steel and concrete weight savings of up to 25% and 60% respectively.
In container applications not only bulk storage of liquid could be cheap- ened through a lower initial cost as well as lower maintenance, but this could equally apply to the bulk storage of solids such as coal, grain, flour and rice.
The concept of tensile membrane dams using ferrocement rather than the gravity or arch principles could also be further explored. However, the biggest possible application forseen by the writer in Hong Kong is in shipping and marine uses.
The marine uses could also imply that in a locality deprived of adequate building space, which has long resorted to living on water in insanitary and uncomfortable "sampan cities", this phenomenon could now be rationaliz- ed; the several shallow bays which exist in the territory could be adapted for floating ferrocement marinas.
Unlike permanently located build- ings, prefabricated floating ferroce- ment dwellings would have the advant- age of easy services and of being able
30
700-800CM
700-800 cm
Typical Russian water conveying trough, 20 mm thick in mass-produced precast ferroce ment units
to be moved as required, within and figures of man hours for typical ferro- without Hong Kong.
The economic incentives
The main incentives for the marine use of ferrocement are economic. At this time too few ferrocement vessels have been built and those which were, comprise the small tonnage variety. It is consequently difficult to make more than an extrapolation from the exist- ing data of the savings possible.
Considering the hull only it would appear that these savings could be sub- stantial, especially in regions which spend vast sums on steel importation. To illustrate this by a similar material, a prestressed concrete barge will have on average about 30% of the steel con- tent of an equivalent one built entirely of steel and a typical R.C. floating dock may have only 10%.
The savings will of course vary from country to country, but a recent Canadian comparison based on 100 ft. fishing vessels placed ferrocement well below in cost when compared with steel, timber or aluminium. The signifi- cant thing about this comparison was that the proportion of hull cost to the overall cost of the vessel grew with the size of the vessel, consequently any savings in hull construction could be appreciably reflected in the overall price.
North America possesses high labour costs and relatively low steel prices. Taking out rough hull cost comparisons based on the available
cement fishing vessels and local labour and material prices, one can quickly conclude that these figures would be even more favourable in Hong Kong than in Canada.
Yet, the prime cost of the hull is not the only saving which could be expected. Equally important is the reduction in hull and superstructure maintenance.
In a steel ship a good proportion of the crew is kept busy, rather ineffi- ciently, chipping and painting. Should crew wages keep on climbing and the land occupations compete successfully in attractiveness and pay, one way out would be to introduce sacrificial steel sizing or even more expensive protec- tive treatments. That protective cover- ing is not cheap can be judged from the report that in one recent super. tanker of 234.000 tons some 600 tons of high grade paint were needed and a "cosmetic treatment" would have to be repeated every two years. Sacrificial sizing as a solution to maintenance problems could in turn mean addi- tional and structurally unnecessary weight to be propelled which would further increase the fuel bills.
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Apart from maintenance - in itself a powerful argument in favour of fer- rocement depreciation, replacement and insurance costs form other poten- tial incentives. This is because all are effected by the technical performance of the material and its prospects for further development.
Far East BUILDER, July 1971